Transparent foils of paper, fabric, webs, and the like



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, Suitable clarifying media are the hydrosols all the colloids'the hydrosols of which are when drying, to form more or less Patented May 3, 1932 FFICE vrxroa nausea AND KURT rnnnznn, or BERLIN, GERMANY TRANSPARENT F OILS OI PAPER, FABRIC,- WEBS, AND THE LIKE No Drawing.

Uur invention relates transparent foils of the like the same.

Application filed April 3,

to improvements in paper, fabric, webs, and

and the method of manufacturing. More particularly our invention has reference to the method described in the copending application for patent of Bausch,

Ser. No. 143,990, filed October 25, 1926, the said method consisting in producing transparent foils by um adapted to pregnated with clarifying medium is pre excess on both sides of the imbuing paper with a medirender the same transparent. As has been described tion for patent,

in the said applicathe paper is thoroughly ima clarifying medium, which ferably applied in excess is maintained during the following treatment of the paper until the finished article is obtained, perfectly so that the fibre material is imbued with the clarifying medium. 1n the method described in the said application of Bausch resins and similar sub stances are used as clarifying media, which clarifying med ia are dissolved in suitable solvents'such as alcohol, aceton, and the like.

in order to carry nomical way, i

the solvents, for

must be made if plosion of the e out the method in an ecois necessary to regenerate which purpose provision or preventing ignition or exvaporated solvents.

The object of the improvements is to provide a method in which incendiary materials are not used, and which can be car=- ried out at redu ced cost. by means of which a better product is obtained, the product being highly transparent and colourless.

lVith this object in view our invention con sists in using hyd rosols of different charac ters as clarifying media in lieu of the resins.

of capable,

clear foils, such for example as albumin,

animal stances of the starch, dextrin, cose (cellulose-Xanthogenate and cellulose-. thiocarbonate) may be used, or

glue, carrageen' moss, further subcharacter of sugar, such as and the like. Further, .VlS-

or xanthogenate of other carbohydrates such as starch-xanthogenate,

example a 30% may be used. For solution of gelatin ha's'been paper, and the said drying thiocarbonate 1928, Serial No. 267,126, and in Germany April 6, 1927. i

found to be useful as a clarifying medium.

A solution of gelatin high concentration is difficult or animal glue of this very viscous, and it is thoroughly to impregnate-the paper by means of such a viscous solution.

By adding aliphatic alcohols the viscosity of the solution can be considerably reduced, the

particularly suitable for The addition of alcohol to the glue solution may be carethyl alcohol being this purpose.

gelatin or animal ried so far that the begins to precipitate.

gelatin or animal glue For the same purpose aromatic alcohols soluble in Water, for example alcohols of the added. An addition ticularly suitable be transparency of the p phenol group, may be of carbolic acid is parcause it improves the roduct. Forimparting the desired pliabilityto the-product a softening medium soluble in Water is added to the clar fying medium. media are sugar, hycharacter, glycerin Suitable softening groscopic salts of any lactic acid, and the like.

For hardening the product and improving" the transparency thereof we prefer to add formic aldehyde substituted aldehydes um. For hardening CH O), urea, and similar to the clarifying medithe surface of the foil and rendering the same proof againstscra'tching, we expose the foil durlng or after the process to the hyde, for which action of formic aldepurpose the foil may be. passed through a bath of formalin solution of formic aldehyde),

(a watery or treated on one or both faces with formalin vapor.

In a modification of the process we addchromium compounds to the hydrosol, or .we subject the foil to a subsequent treatment by means of 'chromic salt solutions, the chromium nitrate Cr(NO to be most appropriate um. For imparting,

'which is particularly the finished foil on both sides with an organosol such as zaponium quer.

having been found as a hardening medi to the foil, a surface hard and good We coat or acetyl cellulose lac- Transparent foils made by our improved process are optically and physically they clear,

are not homogeneous.

Therefore, when drying the same, they tend to form waves, folds a nd stripes. To prevent while chemically.

' dried, until the humidity has been removed to a certain degree. Preferably, the tension of the foils is varied in the course of drying, for example by placing the foils on sheet metal and afterwards bending the said sheet metal into cylindric or similar curved form, 4 so that the paper is put under tension. As

drying continues, the sheet metal is gradual- -ly returned into plane form. By thus subjecting the flexible carrier of the wet foil to different degrees of bending the surface from which the solvent is vaporized is subjected to varying tension, the said varying tension being transmitted to the foil, which therefore can not be formed intowaves.

The said manner of drying the foil may also be used for imparting a surface appearance of different character to the foil. For example, where a very high transparency is desired a carrier such as sheet metal having a smooth and highly polished surface is used. Where a' rough surface is desired we use carriers which are made rough at the surface by corrosion. The said rough carriers are used for example in the manufacture of tracing paper, the result being that the tracing paper readily takes up the ink of the pen or the graphite of the pencil. The tracing paper thus produced has a high transparency.

The foil may further be dried under tension on sheet metal or cylinders by placing the same on the said carrier alternately with its opposite faces. Thereby both faces are made absolutely smooth and plano-parallel, or one or both faces are made rough and capable of taking up ink.

If it is desired to manufacture a tracing paper the surface of the foil is further treated in order that the graphite of lead-pencils is more readily taken up thereby. For this purpose we apply a coating of a suspension of a suitable powder to one or both faces of the foil, preferably while the foil is wet. Preferably, we use a binding medium which provides a protective colloid for the powder suspended in water, for example a hydrosol such as gelatin or dextrin. When using substances containing gliadin (glutin) as a binding medium and protective colloid for the suspension of powder it is preferred to add thereto a hardening medium such as formalin. The best results have been obtained when using a cold suspension of starch grains as a watery suspension of powder, a suitable composition being 100 grccold, suspended wheat starch, 2 gr. animal glue, 0.2 gr. alp a-naphthol. The said starch suspension may be sprayed on the wet foil.

In a modification of thefprocess the surface of the foil is coated with. an organosol such as zaponium lacquer containing the powder in suspension, the result being a foil adapted to be written or drawn upon. Other means may be provided for producing a rough surface on the organosol when drying the same.

In carrying out the method we proceed in the manner described in detail in the afore-' said application for patent of Bausch. We have found that the foil may be made from certain fabrics such as linen. As has been explained in the said application, it is important that the impregnating medium permeates the whole body of the paper linen, fabric, or the like, for which reason it is necessary thoroughly to imbue the paper or fabric with the clarifying medium, care be- Y ing'taken that after impregnation and before drying the paper or fabric is coated on both sides with an excess of the clarifying medium. Preferably, the foil consists of a body of paper which has so much of the impregnating medium applied thereto that an additional. surface layer of the said medium is provided on both sides of the paper, for which purpose an excess of the impregnating medium is applied to the surfaces of the paper and maintained thereon to the end of the manufacture of the foil. Thereby thev surfaces of the foil can be made perfectly plane and parallel to each other, which is necessary for an unimpeded passage of the light rays. Further a film thus prepared is free of minute cavities produced in the interior parts by the drying of the impregnating medium, the parts of the solvent of the impregnating medium escaping when drying the film being replaced by parts of the medium taken from the surface layers. Further, by providing the said surface layers, the hardening of the film by the drying of the impregnating medium is retarded, the said surface layers providing a tight coating re-' tarding evaporation of the solvent and certain softening media added to the impregnated medium. In this respect the property of the outer layers may be improved by properly treating the same, for example by heat, so that the said layers are made sufficiently impermeable to prevent the entire escape 0 some of the components of the solvent of the impregnating medium and other matter.

added thereto for softening the film. Therefore the film remains soft and-flexible for a considerable length of time even if only a small amount of softening media or no soft-.

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surfaces are thereby made hard and tight so as to prevent complete evaporation of the solvent within the paper. A film thus prepared has a very hard surface which cannot be spoilt by scratches, and which therefore can be used for a long time.

For accelerating the impregnating operation we first evacuate the paper before passing the same through the impregnating medium, and when passing the previously evacuated paper through the impregnating bath we hold the bath under high pressure.

In the manufacture of the foil we make use of a strong glued paper having a fine and uniform texture. The paper ought to be free of any filling media such as kaolin. We have found that the best results are ob tained when using a paper made from rags rather than a paper made from wood cellulose, though our invention is not limited to the treatment of paper made from rags.

lln carrying out the process we make use of the apparatus shown and described in the aforesaid application for patent of Bausch.

-We claim:

1. The herein described method of producing flexible transparent or translucent foils, which consists in thoroughly imbuing paper fabric. or the like with a hydrosol of a colloid, the sol of which is adapted upon drying to produce a more or less transparent foil, and immediately thereafter coating the same on both sides with an excess of such hydrosol, so that the paper, fabric or the like is kept in a state of complete impregnation during and to the end of the drying of the hydrosol.

2. The herein described method of producing flexible transparent or translucent foils, which consists in impregnating paper, fabric or the like with a 30 to 50% solution of gelatin containing an agent adapted to reduce viscosity, maintaining an excess of such hydrosol on the sides of the material being treated so as to keep the same in a state of complete impregnation, and drying the same.

3. The herein described method of producing flexible and transparent foils, which consists in impregnating paper, fabric or the like with a hydrosol of a colloid the sol of which is adapted when drying to produce more or less transparent foils and containing a softening agent adapted to be dissolved in or mixed with water, maintaining an excess of such hydrosol on both sides of the material being treated so as to keep the same in a state of complete impregnation, and drying the same;

4. The herein described method of producing flexible transparent or translucent foils,

which consists in impregnating paper, fabric or the like with a hydrosol of a colloid the sol of which is adapted when drying to produce a more or less transparent foil, maintaining an excess of-such hydrosol on both sides of the material being'treated so as to keep the same in a state of complete impregnation, treating the surfaces of said paper with a hardening medium, and drying the paper, fabric or the like.

5. The herein described method of producing flexible transparent or translucent foils, which consists in impregnating paper, fabric or the like with a hydrosol of a colloid the sol of which is adapted when drying to produce a more or less transparentfoil, maintaining an excess of such hydrosol on both sides of the material being treated so as to keep the same in a state of complete impregnation, coating the surfaces of said foil with an organosol, and drying the paper, fabric or the like.

signatures.

VIKTOR BAUSCH. KURT FRENZEL. 

